The specific goal of this study is to understand the effects of gases and moderate gas pressures on protein structure and dynamics. High resolution X-ray crystallography will be used to study in a systematic fashion the detailed interactions of several inert gases (He, Ar, Xe, CF4, SF6, N2) with the oxygen binding and transport proteins myoglobin and hemoglobin. Gas pressure between 1 and 300 atmospheres will be examined with the aid of a newly designed high-pressure crystallographic cell. Experiments are designed to address several questions: 1) Where are the specific gas binding sites in the heme proteins? Are there different sites for different gases? Do the different globins have different sites? 2) What are the structural and dynamic perturbations that gas binding produce? Is there a relationship between the gas properties and the extent of the perturbation? 3) What are the structural and dynamic perturbations of gas pressure? Are these perturbations different from those produced by hydrostatic pressure? 4) What effect does the iron spin state of the protein have on the binding of inert gases? Gases provide a useful probe to study the internal architecture of protein molecules. A crystallographic study of gas binding is the most definitive method to examine packing defects or atom-sized cavities, which are believed to exist within proteins. Knowledge of the role of these cavities in protein dynamics and function and an understanding of the packing interactions within the protein interior will contribute to more intelligent protein design and engineering. Gas binding to blood protein hemoglobin is important in the delivery of gas anaesthetics to the central nervous system. The effects of anaesthetic gases on protein structure and function is still not understood. The pressures examined in this study are in the range which cause narcosis and anaesthesia and that are commonly found in the biosphere. The final goal of this study is to seek a correlation between the gas binding properties as revealed by X-ray crystallography and the biomedical role of these gases.